Comparative analysis of minimal residual disease detection by multiparameter flow cytometry and enhanced ASO RQ-PCR in multiple myeloma

Ixazomib, Lenalidomide, and Dexamethasone (IRD) Treatment with Cytogenetic Risk-Based Maintenance in Transplant-Eligible Myeloma: A Phase 2 Multicenter Study by the Nordic Myeloma Study Group

Scarce data exist on double maintenance in transplant-eligible high-risk (HR) newly diagnosed multiple myeloma (NDMM) patients. This prospective phase 2 study enrolled 120 transplant-eligible NDMM patients. The treatment consisted of four cycles of ixazomib-lenalidomide-dexamethasone (IRD) induction plus autologous stem cell transplantation followed by IRD consolidation and cytogenetic risk-based maintenance therapy with lenalidomide + ixazomib (IR) for HR patients and lenalidomide (R) alone for NHR patients. The main endpoint of the study was undetectable minimal residual disease (MRD) with sensitivity of <10-5 by flow cytometry at any time, and other endpoints were progression-free survival (PFS) and overall survival (OS). We present the preplanned analysis after the last patient has been two years on maintenance. At any time during protocol treatment, 28% (34/120) had MRD < 10-5 at least once. At two years on maintenance, 66% of the patients in the HR group and 76% in the NHR group were progression-free (p = 0.395) and 36% (43/120) were CR or better, of which 42% (18/43) had undetectable flow MRD <10-5. Altogether 95% of the patients with sustained MRD <10-5, 82% of the patients who turned MRD-positive, and 61% of those with positive MRD had no disease progression at two years on maintenance (p < 0.001). To conclude, prolonged maintenance with all-oral ixazomib plus lenalidomide might improve PFS in HR patients.

MRD in multiple myeloma: does CR really matter?

Multiple myeloma embodies the paradigm of the deeper the response, the longer the survival. However, results are conflicting regarding achievement of complete remission (CR) and minimal residual disease (MRD) negativity; some patients with persistent M protein have undetectable MRD. We reviewed the frequency of this discordance and outcomes of these patients. We spotlight possible explanations for and consequences of conflicting response criteria and suggest that MRD be assessed in patients achieving very good partial response or better in clinical trials.

Next-generation sequencing for MRD monitoring in B-lineage malignancies: from bench to bedside

Minimal residual disease (MRD) is considered the strongest relevant predictor of prognosis and an effective decision-making factor during the treatment of hematological malignancies. Remarkable breakthroughs brought about by new strategies, such as epigenetic therapy and chimeric antigen receptor-T (CAR-T) therapy, have led to considerably deeper responses in patients than ever, which presents difficulties with the widely applied gold-standard techniques of MRD monitoring. Urgent demands for novel approaches that are ultrasensitive and provide sufficient information have put a spotlight on high-throughput technologies. Recently, advances in methodology, represented by next-generation sequencing (NGS)-based clonality assays, have proven robust and suggestive in numerous high-quality studies and have been recommended by some international expert groups as disease-monitoring modalities. This review demonstrates the applicability of NGS-based clonality assessment for MRD monitoring of B-cell malignancies by summarizing the oncogenesis of neoplasms and the corresponding status of immunoglobulin (IG) rearrangements. Furthermore, we focused on the performance of NGS-based assays compared with conventional approaches and the interpretation of results, revealing directions for improvement and prospects in clinical practice.

Minimal Residual Disease in Multiple Myeloma: Something Old, Something New

The game-changing outcome effect, due to the generalized use of novel agents in MM, has cre-ated a paradigm shift. Achieving frequent deep responses has placed MM among those neoplasms where the rationale for assessing MRD is fulfilled. However, its implementation in MM has raised specific questions: how might we weight standard measures against deep MRD in the emerging CAR-T setting? Which high sensitivity method to choose? Are current response criteria still useful? In this work, we address lessons learned from the use of MRD in other neoplasms, the steps followed for the harmonization of current methods for comprehensively measuring MRD, and the challenges that new therapies and concepts pose in the MM clinical field.

A large meta-analysis establishes the role of MRD negativity in long-term survival outcomes in patients with multiple myeloma

The prognostic value of minimal residual disease (MRD) for progression-free survival (PFS) and overall survival (OS) was evaluated in a large cohort of patients with multiple myeloma (MM) using a systematic literature review and meta-analysis. Medline and EMBASE databases were searched for articles published up to 8 June 2019, with no date limit on the indexed database. Clinical end points stratified by MRD status (positive or negative) were extracted, including hazard ratios (HRs) on PFS and OS, P values, and confidence intervals (CIs). HRs were estimated based on reconstructed patient-level data from published Kaplan-Meier curves. Forty-four eligible studies with PFS data from 8098 patients, and 23 studies with OS data from 4297 patients were identified to assess the association between MRD status and survival outcomes. Compared with MRD positivity, achieving MRD negativity improved PFS (HR, 0.33; 95% CI, 0.29-0.37; P < .001) and OS (HR, 0.45; 95% CI, 0.39-0.51; P < .001). MRD negativity was associated with significantly improved survival outcomes regardless of disease setting (newly diagnosed or relapsed/refractory MM), MRD sensitivity thresholds, cytogenetic risk, method of MRD assessment, depth of clinical response at the time of MRD measurement, and MRD assessment premaintenance and 12 months after start of maintenance therapy. The strong prognostic value of MRD negativity and its association with favorable outcomes in various disease and treatment settings sets the stage to adopt MRD as a treatment end point, including development of therapeutic strategies. This large meta-analysis confirms the utility of MRD as a relevant surrogate for PFS and OS in MM.

Validation of a PCR-Based Next-Generation Sequencing Approach for the Detection and Quantification of Minimal Residual Disease in Acute Lymphoblastic Leukemia and Multiple Myeloma Using gBlocks as Calibrators

Detection of minimal residual disease (MRD) to guide therapy has been a standard practice in treatment of childhood acute lymphoblastic leukemia (ALL) for decades. In multiple myeloma (MM), a clear correlation is found between absence of MRD and longer survival. Quantitative allele-specific oligonucleotide (qASO)-PCR is the standard molecular method for MRD detection in these hematologic malignant tumors. However, this technique has some drawbacks that can be overcome by next-generation sequencing (NGS). In this study, NGS is validated as an alternative method for qASO-PCR for MRD detection in both ALL and MM. MRD results obtained by NGS and qASO-PCR were compared in 59 and 39 bone marrow samples of 33 and 14 patients with ALL and MM, respectively. Our results indicate that the use of gBlocks as calibrators makes the NGS approach a powerful tool to quantify MRD. With an input of 400 ng of DNA (corresponding to approximately 7 × 10⁴ cells), a limit of detection of 0.01% can be achieved. The specificity of the NGS-MRD technique was 100%, and a correlation with qASO-PCR for quantifiable MRD results of 0.93 and 0.91 was found in ALL and MM, respectively. Especially for MM, the higher applicability (100%) of the NGS-MRD protocol, compared with qASO-PCR (57%), was clearly demonstrated. These results demonstrate that NGS is an even better alternative to qASO-PCR.

Minimal Residual Disease in Multiple Myeloma: Current Landscape and Future Applications With Immunotherapeutic Approaches

The basic principle that deeper therapeutic responses lead to better clinical outcomes in cancer has emerged technologies capable of detecting rare residual tumor cells. The need for ultra-sensitive approaches for minimal residual disease (MRD) detection is particularly evident in Multiple Myeloma (MM), where patients will ultimately relapse despite the achievement of complete remission, which is commonplace due to remarkable therapeutic advances. Consequently, current response criteria on MM have been amended based on MRD status and MRD negativity is now considered the most dominant prognostic factor and the most valuable indicator for a subsequent relapse. However, there are particular limitations and several aspects for MRD assessment that remain open. This review summarizes current data on MRD in the clinical management of MM, highlights open issues and discusses the challenges and the endless opportunities arising for both patients and clinicians. Furthermore, it focuses on the current status of MRD in clinical trials, its dynamics in addressing debatable aspects in the clinical handling and its potential role as the prevailing factor for future MRD-driven tailored therapies.

Minimal Residual Disease Negativity Does Not Overcome Poor Prognosis in High-Risk Multiple Myeloma: A Single-Center Retrospective Study

BACKGROUND

Minimal residual disease (MRD) is a standard measurement for response assessment in multiple myeloma (MM). Despite new treatments, high-risk MM patients continue to have poor prognosis. We evaluated the effect of MRD negativity in high-risk versus standard-risk patients.

PATIENTS AND METHODS

We retrospectively evaluated all consecutive MM patients who underwent routine MRD testing by 1-tube 8-color advanced flow cytometry with 2,000,000 events and sensitivity level 10^-5 at our center from 2015 to 2018 after initial therapy. Kaplan-Meier and log-rank test were used to assess survival estimates and differences between study groups.

RESULTS

One hundred thirty-six patients with MRD testing after initial therapy or autologous stem-cell transplantation were identified. At a median follow-up of 14 months (range, 1-36 months), progression-free survival and overall survival were significantly worse in high-risk versus standard-risk patients. During the study period, 50% of high-risk group had experienced disease progression (relapse and/or death) versus 20% in the standard-risk group (P = .0006). No patients with standard-risk died, but 4 (14%) in the high-risk group did (P = .0007). Regardless of MRD status, high-risk patients had statistically significant worse progression-free survival than standard-risk patients. At median follow-up, those with disease 10% standard-risk/MRD negative; 20% standard-risk/MRD positive; 40% high-risk/MRD negative; and 45% high-risk/MRD positive had either experienced relapse or died (P = .0041). MRD status did not significantly affect overall survival in either group (P = .0914); however, longer follow-up is needed to assess survival.

CONCLUSION

Genetic abnormalities remain a powerful prognostic indicator for MM, regardless of MRD status. For newly diagnosed MM patients treated with novel triple-drug initial therapy and frontline autologous stem-cell transplantation, MRD-negative status did not mitigate the poor-prognosis outcomes of high-risk MM patients.

Ficolled bone marrow is superior to bone marrow buffy coat for detection of minimal residual disease in multiple myeloma

OBJECTIVE

Buffy coat and ficoll of bone marrow (BM) are viable options for the study of minimal residual disease (MRD) in multiple myeloma (MM). As yet, there is no data about the superiority of either sample types. Herein, we aimed to address this issue.

METHODS

Forty pairs of ficolled BMs and BM buffy coats of 19 MM patients were studied for MRD by allele-specific oligonucleotide real-time quantitative PCR, with patient-specific primers/probes whenever appropriate.

RESULTS

There were 41 pairs of MRD data for comparison analysis due to one patient with biclonal disease. MRD levels in ficolls and buffy coats were highly concordant (r_s = 0.936, P < 0.0001), with 31 (76%) and seven (17%) pairs being concomitantly MRD-positive or -negative. On the other hand, apart from the 16 pairs being both MRD-negative, or -positive but not quantifiable in ficolls and buffy coats, majority (n = 22, 88%) had higher MRD levels in ficolled BMs than BM buffy coats. Furthermore, in 17 pairs, in which MRD was quantifiable in both, MRD levels in ficolled BMs were 3.1 times those of BM buffy coats (median, 567/10⁵ vs. 184/10⁵, P = 0.001).

CONCLUSION

Taken together, ficolled BM is more sensitive than BM buffy coat for MRD detection in MM, hence should be recommended.

RVD induction and autologous stem cell transplantation followed by lenalidomide maintenance in newly diagnosed multiple myeloma: a phase 2 study of the Finnish Myeloma Group

Autologous stem cell transplantation (ASCT) combined with novel agents is the standard treatment for transplant-eligible, newly diagnosed myeloma (NDMM) patients. Lenalidomide is approved for maintenance after ASCT until progression, although the optimal duration of maintenance is unknown. In this trial, 80 patients with NDMM received three cycles of lenalidomide, bortezomib, and dexamethasone followed by ASCT and lenalidomide maintenance until progression or toxicity. The primary endpoint was the proportion of flow-negative patients. Molecular response was assessed if patients were flow-negative or in stringent complete response (sCR). By intention to treat, the overall response rate was 89%. Neither median progression-free survival nor overall survival (OS) has been reached. The OS at 3 years was 83%. Flow-negativity was reached in 53% and PCR-negativity in 28% of the patients. With a median follow-up of 27 months, 29 (36%) patients are still on lenalidomide and 66% of them have sustained flow-negativity. Lenalidomide maintenance phase was reached in 8/16 high-risk patients but seven of them have progressed after a median of only 6 months. In low- or standard-risk patients, the outcome was promising, but high-risk patients need more effective treatment approach. Flow-negativity with the conventional flow was an independent predictor for longer PFS.

Impact of Minimal Residual Disease Detection by Next-Generation Flow Cytometry in Multiple Myeloma Patients with Sustained Complete Remission after Frontline Therapy

Minimal residual disease (MRD) was monitored in 52 patients with sustained CR (≥2 years) after frontline therapy using next-generation flow (NGF) cytometry. 25% of patients initially MRD- reversed to MRD+. 56% of patients in sustained CR were MRD+; 45% at the level of 10⁻⁵; 17% at 10⁻⁶. All patients who relapsed during follow-up were MRD+ at the latest MRD assessment, including those with ultra-low tumor burden. MRD persistence was associated with specific phenotypic profiles: higher erythroblasts’ and tumor-associated monocytes/macrophages’ predominance in the bone marrow niche. NGF emerges as a suitable method for periodic, reproducible, highly-sensitive MRD-detection at the level of 10⁻⁶.

Minimal Residual Disease Assessment Within the Bone Marrow of Multiple Myeloma: A Review of Caveats, Clinical Significance and Future Perspectives

There is an increasing clinical interest in the measure and achievement of minimal residual disease (MRD) negativity in the bone marrow of Multiple Myeloma (MM) patients, as defined equally either by Multicolor Flow Cytometry (MFC) or by Next Generation Sequencing (NGS) technologies. At present, modern technologies allow to detect up to one on 104 or on 105 or even on 106 cells, depending on their throughput. MFC approaches, which have been progressively improved up to the so-called Next Generation Flow (NGF), and NGS, which proved clear advantages over ASO-PCR, can detect very low levels of residual disease in the BM. These methods are actually almost superimposable, in terms of MRD detection power, supporting the lack of unanimous preference for either technique on basis of local availability. However, some technical issues are still open: the optimal assay to use to detect either phenotype (e.g., next generation multidimensional flow cytometry, imaging) or genotype aberrations (e.g., ASO-RQ PCR, digital droplet PCR, NGS) and their standardization, the sample source (BM or peripheral blood, PB) and its pre-processing (red-cell lysis vs. Ficoll, fresh vs. frozen samples, requirement of CD138+ cells enrichment). Overall, MRD negativity is considered as the most powerful predictor of favorable long-term outcomes in MM and is likely to represent the major driver of treatment strategies in the near future. In this manuscript, we reviewed the main pitfalls and caveats of MRD detection within bone marrow in MM patients after front-line therapy, highlighting the improving of the currently employed technology and describing alternative methods for MRD testing in MM, such as liquid biopsy.

Minimal Residual Disease in Multiple Myeloma: Impact on Response Assessment, Prognosis and Tumor Heterogeneity

Multiple Myeloma (MM) therapy has evolved rapidly over the past decade. With current multidrug combinations and autologous transplant, rates of overall response exceed 90% and complete response (CR) more than 50% in some studies. Unfortunately, despite higher rates of CR, relapse rates remain high suggesting that persistent disease may not be measured by current techniques. Traditionally, response rates were defined by urine and serum protein electrophoresis, immunofixation and histopathological absence of clonal plasma cells in the bone marrow. Currently, there are several validated sensitive assays to evaluate for MRD (minimal residual disease); multiparameter flow cytometry (MFC) including nextgeneration flow cytometry (NGF), next-generation sequencing (NGS), and allele specific oligonucleotide quantitative polymerase chain reaction (ASO-qPCR). These methods have provided a means to quantitatively assess residual disease and accurately prognosticate PFS and OS in myeloma. In this chapter, we will discuss the current techniques for MRD detection as well as describe techniques that are emerging for improved characterization of drug resistant residual populations that could be adapted for MRD monitoring in the future. While improved therapies are able to eradicate the dominant clone, resistant sub-clones persist and remain undetectable even by MRD techniques. Characterization of these clones will help design therapies against drug-resistant clones and move us closer to a cure in MM.

Standardized assay for assessment of minimal residual disease in blood, bone marrow and apheresis from patients with plasma cell myeloma

The recent advances in myeloma treatment result in significantly better outcomes, defined as increased progression free survival (PFS) and overall survival (OS). Since there is a proven correlation between the extend of response and prolonged survival, there is an urgent need for highly sensitive assays for the detection of minimal residual disease (MRD). Next generation flow cytometry has become a valuable approach for sensitive evaluation of the depth of complete response (CR). Here, we report the diagnostic performance and validation results of a single-tube 9-color panel assay. The validation design included intra-assay analysis measuring accuracy, inter-assay analysis estimating method’s linearity and precision and inter-assay analysis evaluating repeatability. Furthermore, in inter-operator analysis assessed the comparability of the result analysis of different operators. Staining stability was evaluated in age-of-stain experiments. Our validation results show that a reliable detection of residual myeloma cells is feasible to a detection level of 10⁻⁵ with a single-tube assay for a variety of materials (peripheral blood, bone marrow and stem cell apheresis). This study establishes highly sensitive, fully standardized approach for MRD detection in myeloma that is ready for implementation in routine diagnostic laboratories.

Molecular detection of minimal residual disease in multiple myeloma

Despite the significantly higher complete remission rates and improved survival achieved in the last decade, multiple myeloma (MM) patients continue to relapse due to persistence of minimal residual disease (MRD). Generally, MRD refers to persistence of low levels of disease in the order of one tumour cell in ≥10⁵ normal cells. Currently, molecular and immunophenotypic techniques are employed for MRD detection. This review focuses on MRD detection by molecular techniques, including allele-specific oligonucleotide polymerase chain reaction (ASO-PCR), next-generation sequencing (NGS) and digital PCR (dPCR), in addition to a brief description of, and comparison with, multiparameter flow cytometry. The basic principles, technical advantages and limitations, and the clinical impact of all three molecular techniques are reviewed and compared. They all have a sensitivity of at least 10^-5 , among which ASO real-time quantitative PCR is the most well-standardized, and NGS carries the highest sensitivity and applicability, while dPCR is still under investigation. Furthermore, molecular MRD negativity is a favourable prognostic factor for survival of patients with MM. However, several challenges inherent to molecular detection of MRD still remain to be overcome, particularly false negativity and failure to detect extramedullary disease. Finally, detection of MRD from peripheral blood remains challenging.

BMT CTN Myeloma Intergroup Workshop on Minimal Residual Disease and Immune Profiling: Summary and Recommendations from the Organizing Committee

The Blood and Marrow Transplant Clinical Trials Network Myeloma Intergroup Workshop on Minimal Residual Disease and Immune Profiling was convened on December 1, 2016 at the American Society of Hematology meeting to discuss the emerging data and technologies for minimal residual disease assessment and immune profiling in myeloma. Particular emphasis was placed on developing strategies to incorporate these techniques into clinical trial design. This document reviews the literature, summarizes the topics discussed in the workshop, and provides recommendations for integration of these techniques into future clinical trial design.

Minimal residual disease in multiple myeloma: Benefits of flow cytometry

Over the last 20 years, the approaches to the treatment of multiple myeloma (MM) have changed considerably, which led to an increase in remission rate. Using new diagnostic methods has made it possible to assess the response to treatment more reliably and forecast disease recurrence: allele-specific polymerase chain reaction, new-generation sequencing and multicolor flow cytometry enable minimal residual disease (MRD) detection of with sensitivity of 10^-5 to 10^-6 . MRD assessment with flow cytometry using is a rapidly developing area of research. The goal of multicenter groups that use flow cytometry as a tool to detect MRD in patients with MM is achieving standardization and increasing sensitivity and specificity of this method. This article provides data about the methods used for MRD monitoring and describes the advances in the field of flow cytometry.

Standardisation of minimal residual disease in multiple myeloma

The assessment of the effectiveness of chemotherapy in oncology cannot disregard the concept of minimal residual disease (MRD). In fact, the efforts of numerous scientific groups all over the world are currently focusing on this issue, with the sole purpose of defining sensitive, effective assessment criteria that are, above all, able to give acceptable, easily repeatable results worldwide. Regarding this issue, especially with the advent of new drugs, multiple myeloma is one of the haematologic malignancies for which a consensus has not yet been reached. In this review, we analyse various techniques that have been used to improve the sensitivity of response, aimed at reducing the cut-off values previously allowed, as well as serological values like serum-free light chain, or immunophenotypic tools on bone marrow or peripheral blood, like multi-parameter flow cytometry, or molecular ones such as allele-specific oligonucleotide (ASO)-qPCR and next-generation/high-throughput sequencing technologies (NGS). Moreover, our discussion makes a brief reference to promising techniques, such as mass spectrometry for identifying Ig light chain (LC) in peripheral blood, and the assessment of gene expression profile not only in defining prognostic risk at the diagnosis but also as a tool for evaluation of response.

The Role of Minimal Residual Disease Testing in Myeloma Treatment Selection and Drug Development: Current Value and Future Applications

Treatment of myeloma has benefited from the introduction of more effective and better tolerated agents, improvements in supportive care, better understanding of disease biology, revision of diagnostic criteria, and new sensitive and specific tools for disease prognostication and management. Assessment of minimal residual disease (MRD) in response to therapy is one of these tools, as longer progression-free survival (PFS) is seen consistently among patients who have achieved MRD negativity. Current therapies lead to unprecedented frequency and depth of response, and next-generation flow and sequencing methods to measure MRD in bone marrow are in use and being developed with sensitivities in the range of 10^-5 to 10^-6 cells. These technologies may be combined with functional imaging to detect MRD outside of bone marrow. Moreover, immune profiling methods are being developed to better understand the immune environment in myeloma and response to immunomodulatory agents while methods for molecular profiling of myeloma cells and circulating DNA in blood are also emerging. With the continued development and standardization of these methodologies, MRD has high potential for use in gaining new drug approvals in myeloma. The FDA has outlined two pathways by which MRD could be qualified as a surrogate endpoint for clinical studies directed at obtaining accelerated approval for new myeloma drugs. Most importantly, better understanding of MRD should also contribute to better treatment monitoring. Potentially, MRD status could be used as a prognostic factor for making treatment decisions and for informing timing of therapeutic interventions. Clin Cancer Res; 23(15); 3980-93. ©2017 AACR.

Next Generation Flow for highly sensitive and standardized detection of minimal residual disease in multiple myeloma

Flow cytometry has become a highly valuable method to monitor minimal residual disease (MRD) and evaluate the depth of complete response (CR) in bone marrow (BM) of multiple myeloma (MM) after therapy. However, current flow-MRD has lower sensitivity than molecular methods and lacks standardization. Here we report on a novel next generation flow (NGF) approach for highly sensitive and standardized MRD detection in MM. An optimized 2-tube 8-color antibody panel was constructed in five cycles of design-evaluation-redesign. In addition, a bulk-lysis procedure was established for acquisition of ⩾10⁷ cells/sample, and novel software tools were constructed for automatic plasma cell gating. Multicenter evaluation of 110 follow-up BM from MM patients in very good partial response (VGPR) or CR showed a higher sensitivity for NGF-MRD vs conventional 8-color flow-MRD -MRD-positive rate of 47 vs 34% (P=0.003)-. Thus, 25% of patients classified as MRD-negative by conventional 8-color flow were MRD-positive by NGF, translating into a significantly longer progression-free survival for MRD-negative vs MRD-positive CR patients by NGF (75% progression-free survival not reached vs 7 months; P=0.02). This study establishes EuroFlow-based NGF as a highly sensitive, fully standardized approach for MRD detection in MM which overcomes the major limitations of conventional flow-MRD methods and is ready for implementation in routine diagnostics.

Role of MRD status in relation to clinical outcomes in newly diagnosed multiple myeloma patients: a meta-analysis

Driven by access to better drugs, on average, newly diagnosed multiple myeloma patients have over 10 years overall survival. Using modern combination therapies – with or without the addition of high-dose melphalan and autologous stem cell transplantation – up to 80% of patients reach a complete response. As a logical and necessary step forward, clinical studies have explored strategies to detect minimal residual disease (MRD) and its correlation with clinical outcomes. In this context, MRD has been proposed as a regulatory endpoint for drug approval in newly diagnosed multiple myeloma. To better define the role of MRD negativity in relation to clinical outcomes, we undertook a meta-analysis including published clinical trials of newly diagnosed multiple myeloma patients. We applied a random effects model which weighted studies using the inverse-variance method. Studies were combined on the scale of the logarithm of the hazard ratio (HR) and the corresponding standard error. We found that remaining MRD positive was associated with worse progression-free survival (HR=2.85; 95% confidence interval (CI) 2.17–3.74; P<0.001) and overall survival (HR=2.08; 95% CI 1.44–3.01; P<0.001). Our results show that MRD negativity is a strong predictor of clinical outcomes, supportive of MRD becoming a regulatory endpoint for drug approval in newly diagnosed multiple myeloma.

Multiple Myeloma Minimal Residual Disease

Assessment of minimal residual disease (MRD) is becoming standard diagnostic care for potentially curable neoplasms such as some acute leukemias as well as chronic myeloid and lymphocytic leukemia. Although multiple myeloma (MM) remains as an incurable disease, around half of the patients achieve complete remission (CR), and recent data suggests increasing rates of curability with "total-therapy-like" programs. This landscape is likely to be improved with the advent of new antibodies and small molecules. Therefore, conventional serological and morphological techniques have become suboptimal for sensitive evaluation of highly effective treatment strategies. Although, existing data suggests that MRD could be used as a biomarker to evaluate treatment efficacy, help on therapeutic decisions, and act as surrogate for overall survival, the role of MRD in MM is still a matter of extensive debate. Here, we review the different levels of remission used to define depth of response in MM and their clinical significance, as well as the prognostic value and unique characteristics of MRD detection using immunophenotypic, molecular, and imaging techniques. Key facts The higher efficacy of new treatment strategies for MM demand the incorporation of highly sensitive techniques to monitor treatment efficacy MRD could be used as a more potent surrogate biomarker for survival than standard CR We need to understand the pros and cons of the different MRD techniques The time has come to incorporate highly sensitive, cost-effective, readily available, and standardized MRD techniques into clinical trials to assess its role in therapeutic decisions.

New criteria for response assessment: role of minimal residual disease in multiple myeloma

Assessment of minimal residual disease (MRD) is becoming standard diagnostic care for potentially curable neoplasms such as acute lymphoblastic leukemia. In multiple myeloma (MM), the majority of patients will inevitably relapse despite achievement of progressively higher complete remission (CR) rates. Novel treatment protocols with inclusion of antibodies and small molecules might well be able to further increase remission rates and potentially also cure rates. Therefore, MRD diagnostics becomes essential to assess treatment effectiveness. This review summarizes reports from the past 2 decades, which demonstrate that persistent MRD by multiparameter flow cytometry, polymerase chain reaction, next-generation sequencing, and positron emission tomography/computed tomography, predicts significantly inferior survival among CR patients. We describe the specific features of currently available techniques for MRD monitoring and outline the arguments favoring new criteria for response assessment that incorporate MRD levels. Extensive data indicate that MRD information can potentially be used as biomarker to evaluate the efficacy of different treatment strategies, help on treatment decisions, and act as surrogate for overall survival. The time has come to address within clinical trials the exact role of baseline risk factors and MRD monitoring for tailored therapy in MM, which implies systematic usage of highly sensitive, cost-effective, readily available, and standardized MRD techniques.